References
Microsoft MS-DOS User's Guide and User's Reference, Microsoft Corporation, Redmond, Wash., Document No. 410630001-330-R09-0787. PA0 Advanced MS-DOS Programming, Second Edition, 1988, Ray Duncan, Microsoft Press, Redmond, Wash. ISBN 1-55615-156-8. (Hereinafter referred to as "Duncan".)
In recent years the "personal computer" (PC) has become a very common adjunct to the computing scene. A PC may be loosely defined as a computer system that may be purchased for under five-thousand dollars and which occupies, at most, only a portion of a desktop.
While numerous embodiments of PC's abound, most fall into two categories: 1) those manufactured by Apple Computer Company; and 2) those manufactured by International Business Machines Corporation (IBM) and the numerous "clones" thereof, i.e., machines manufactured by other than IBM, but compatible with IBM's PC's. The IBM-compatible category includes several variants, widely known as the "PC", the "PC-XT", and the "PC-AT", which can all generally run the same programs but which differ in execution speed. Virtually all such machines utilize an operating system known as "MS-DOS", supplied by Microsoft Corporation of Redmond, Wash. The present application is slanted toward the IBM-compatible genre of PC's.
Prior to the introduction of PC's into the workplace, many work environments already had computing systems comprising mainframe computers to which a plurality of terminals were connected (as by a Local Area Network, or "LAN"). A plurality of users would each have a terminal conveniently near, as on their desks. To gain the advantages of PC's without having to sacrifice any of the advantages of the mainframe systems (e.g., access to programs that were written for the mainframe, probably in a programming language not compatible with the PC), and without having to resort to the expense and inconvenience of placing both a terminal and a PC on a user's desk, it became commonplace to provide PC's with "terminal emulation" software. This provides a user with the option of using his PC in free-standing mode, or, by running the terminal emulation program, of using his PC as a terminal connected to the mainframe.
One drawback of this mode of operation is that the terminal emulation program may take up quite a bit of the available RAM (random-access memory) space in the PC, and thus may not leave sufficient space for other programs to run in the PC at the same time. For example, if a user is using his PC in terminal emulation mode to access a desktop publishing program in the mainframe, and if the desktop publishing program wishes to display a "graphic" to the user on his monitor, there may not be sufficient RAM space in the PC for the terminal emulation software and the graphics display software at the same time. This would make it incumbent upon the user, after the graphics information had been forwarded from the mainframe, to exit from the terminal emulation program, run the graphics software in the PC to display the graphic, and then resume operation of the terminal emulation software.
Ways have been sought to allow the mainframe to effect this control of program ordering in the remote PC's, but none have become readily available. The nearest thing provided is the "batch processing" function within MS-DOS. (See, generally, Chapter 4 (pp. 131 et. seq.) of the MS-DOS User's Reference.) This function allows the creation of a "batch file" containing a sequence of MS-DOS commands which will then be sequentially executed. Since the batch file can include commands to run particular programs, this does allow for a sequence of programs to be run. However, the sequence of programs is fixed at the time the batch file is created, and there is no provision to dynamically modify it. It is thus of little value in an interactive scenario in which the order in which it will be desired to run programs is not known ahead of time.